One of the most common forms of information storage apparatus is the magnetic disk file in which information is written on and reproduced from the surface of a rotating storage disk by means of a transducing head. The disk media may be rigid or flexible and storage may be achieved by optical or magnetic means, for example. It is common, particularly in magnetic recording, to support the transducing head very close to the disk medium by means of an air bearing created by the motion of the disk. To access information on different areas of the disk, it is also well known to provide linear or rotary head positioning apparatus to move the heads over the disk surface to different radial positions. The heads are supported over the disk surface by means of support arms mounted on the positioning apparatus in cantilever fashion. The heads are mounted on the support arms by means of compliant suspensions which allow limited motion of the heads to accommodate irregularities in the disk surface or variations in the air bearing.
Vibration or resonance of the support arms can have a deleterious effect on the performance of the information storage apparatus. The introduction of damping to limit vibration in order to prevent the head from striking the disk is discussed in an article entitled "Damped Slider Mount" by R. R. Rynders et al (IBM Technical Disclosure Bulletin, Volume 11, No. 3, August 1968, page 248). A magnetic head, which is fixed rather than movable over a disk, is mounted on the tip of a cantilever support arm which is a sandwich structure of two metal members and a constrained elastomeric damping layer parallel to the disk.
In case of a movable head, it is well known to employ a closed loop servo system to control the positioning apparatus to position the head accurately over a desired concentric track of recorded information on the disk. Vibration of the head support arm can cause the head to move off track and introduce an error signal into the servo system which is modulated at the vibration frequency. Also, the resonant frequency of the head support arm is such as to cause instability of the servo system. Another effect of resonance of a head support arm is the degradation of the signal from the transducing head by modulation of the transduced signal. In the publication entitled "Damped Head Arm" by R. E. Norwood (IBM Technical Disclosure Bulletin, Volume 21, Number 8, January 1979, page 3093), a constrained layer damping technique is described to overcome both these problems. As in the Rynders et al article, the constrained layer is parallel to the plane of the disk and absorbs energy by bending to effect the damping.
Damping of head support arms employed in multiple flexible disk files for similar reasons is described in U.S. Pat. Nos. 4,189,759 (R. C. Bauck et al) and 4,208,684 (D. M. Janssen et al). Both patents show an articulated support arm in which a base portion is hinged to a tip portion by a leaf spring. Up and down motion of the tip portion is damped by a further leaf spring in rubbing contact with friction pads.
Damping has also been employed in different though related areas of disk files such as the head positioning apparatus itself. U.S. Pat. No. 4,144,466 (M. R. Hatch) shows a two part linear actuator for positioning heads radially with respect to the disks. Damping of longitudinal resonances in the actuator is provided by a cylindrical layer of damping material between the two parts through which actuator forces are transmitted in shear. No damping of the head support arms themselves is shown.